spac
3
n 0 * -1 
0.001000
1 2 
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
n 1 ac 0 
10 11 8 7 6 1 9 5 4 3 2 0
n 2 ac 0 
15 14 13 12
